In general, microphones, which convert sound into an electric signal, have been recently increasingly downsized, and accordingly, a microphone using a MEMS (Micro Electro Mechanical System) has been developed.
Such a MEMS resists humidity and heat, as compared with ECMs (Electret Condenser Microphones) of the related art, and downsizing and integrating with a signal process circuit are possible.
Two known types of MEMS microphones are a capacitive MEMS microphone and a piezoelectric MEMS microphone.
A capacitive MEMS microphone generally includes a fixed membrane and a diaphragm, so when a sound pressure is applied from the outside, the gap between the fixed membrane and the diaphragm changes and the capacitance accordingly changes.
The sound pressure is measured on the basis of an electrical signal generated in this process.
On the other hand, a piezoelectric MEMS microphone includes only a vibrating membrane, in which when the vibrating membrane is deformed by external sound pressure, and an electrical signal is generated by a piezoelectric effect, thereby measuring sound pressure.
MEMS microphones can be classified into a non-directional (omnidirectional) microphone and a directional microphone in accordance with the directional characteristic, and directional microphones can be classified into a bidirectional microphone and a unidirectional microphone.
The bid-directional microphone receives sounds from both the front and back, but attenuates sounds from sides, so it has a ribbon polar pattern for sound.
Further, the bidirectional microphone has a good near field effect, so it is generally used by announcers at stadiums with a lot of noise.
On the other hand, the unidirectional microphone maintains output in response to sound from a wide area, but offsets output for sound from the back, thereby improving the S/N ratio, and accordingly, it produces clear sound and is generally used for equipment for recognizing voice.
However, the price of the directional MEMS microphones is increased by over double due to requirement of two or more digital MEMS microphones and DSP (Digital Signal Processing) chips.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.